1. Field of the Invention
The present invention relates generally to power drills that can selectively drive any of a number of plural bits carried by the drill. More particularly, the present invention relates to hand-held power drills that can load and retract in a common chuck, selected ones of rotary tool bits stored in a rotatable magazine within the drill housing.
2. Description of the Prior Art
While the conventional power drill has been a simple, practical and effective tool in many respects, it is apparent that where productivity is of a prime concern, such as in production work and construction, the changing of tool bits can be time consumptive and costly. The conventional portable power drill typically has a three jaw chuck assembly in which a selected tool bit can be mounted and removed manually by using a chuck key. It was recognized that an appreciable amount of time can be extended in the steps of locating the appropriate chuck key, loosening the chuck, removing the tool bit and finding the desired replacement bit, inserting it in the chuck and tightening the chuck, and then perhaps returning the replaced drill bit and the chuck key to storage. The alternative of having more than one power drill, each mounting a different tool bit, has proven to be expensive. Even with the development of keyless chucks where no key is necessary to operate the chuck jaws, it is noted that one must still manually grasp the chuck.
U.S. Pat. No. 2,303,565 to Luna is an example of an early attempt to alleviate this problem. Here, a plural chuck head assembly is mounted at the front of a drill, and is shiftable about a transverse axis to bring a selected chuck head into drive connection with the output shaft of an electric drive. While this arrangement theoretically decreased the time for tool selection and changing, it is apparent that in a practical sense the design will be limited to two or three such chuck heads. Furthermore, it remains necessary for a chuck key to be used for these chuck heads.
Later on there developed power drills with true multi-bit capability, the basic concept of which is exemplified by the device of U.S. Pat. No. 2,679,770 to Carter et al. which employed a multi-chambered cylinder assembly attached to the front of a drill, each chamber having a tool holder for a tool bit of a different size or type. The cylindrical magazine is rotatable about a longitudinal axis to bring a selected tool bit holder in alignment with an axial driving shaft that can be coupled with the selected holder. Efforts at improving upon this configuration of the multiple bit drill were seen in U.S. Pat. No. 5,022,131 to Hobbs and British Patent 1,073,681. Unfortunately these drills suffered from, among other things, alignment problems, and problems stemming from exposure of the cylindrical magazine to dust and other contaminants commonly found in the work environment. A somewhat different approach was tried in McKinze, U.S. Pat. No. 5,065,498. Here a cylindrical magazine was enclosed within the drill housing, and mounted to the rear of a common chuck assembly, a single bit being selectable and advanced within the chuck using a bolt action. A bit is removed from the chuck by retraction of the bolt, however, like the standard drill, a chuck key is required to loosen and tighten the chuck assembly using of this device. This line of development has led to the automated feeding system shown in U.S. Pat. No. 4,604,005 to Russ. Unfortunately such a drill is complex, and would be expensive to fabricate, and is over reliant on its electrically powered key components such as plural electric clutches, load switch and indicator lights, for instance.